Interferon is known to be a family of related proteins characterized notably by antiviral activities.
It has been observed that the antiviral action of interferon is mediated by the synthesis of specific proteins. Specific assays for these proteins have allowed to identify the function of two of them, both enzymes (Baglioni C., 1979, Interferon induced enzymatic activities and their role in the antiviral state, Cell 17, 255-64). One of these enzymes is an oligonucleotide polymerase. This oligonucleotide polymerase forms from ATP short chains of adenosines linked by 2'.fwdarw.5' phosphodiester bonds (Kerr I. M. and Brown R. E., 1978, pppA2'p5'A2'p5'A: An inhibitor of protein synthesis synthesized with an enzyme fraction from interferon treated cells, PNAS 75, 256-60), which have been designated by 2'-5' oligoadenylates. One of these 2',5' oligoadenylates can be represented by the following formula: ##STR1##
It is composed of short chains containing several adenosine groups (adenine+ribose), linked with one another by 2'-5' phosphodiester bonds, as shown and in which the 5' position of the adenine nucleus of the terminal adenosine is linked to a various number of phosphate groups (up to three on the above represented 2'.fwdarw.5' oligoadenylate). When the above represented 2'.fwdarw.5' oligoadenylate is entirely dephosphorylated, that is when the phosphate group linked to the 5' position of the adenine nucleus of the terminal adenosine is freed from said various number of phosphate groups, the resulting compound is designated by "(2'.fwdarw.5')A.sub.3 core", which is an abbreviation for "riboadenylyl (2'.fwdarw.5')riboadenylyl 2'.fwdarw.5')riboadenosine core". It will be understood that the expression "2'-5' oligoadenylate" as mentioned above and as used hereafter shall, as a matter of convenience of language, be understood as also including the partially dephosphorylated or entirely dephosphorylated, i.e. the (2'.fwdarw.5')A.sub.3 core.
It must be pointed out that in the following of the description, all the chemical compounds are designated under the French chemical nomenclature.
The discovery of these 2'-5' oligoadenylates revealed a new class of biologically active oligonucleotides deemed to have an important role as mediators of the action of interferon, notably in the activation of endoribonuclease which is present as well in interferon treated cells as in interferon non treated cells, and in the inhibition of protein synthesis. But the 2'.fwdarw.5'phosphodiester bonds of these adenylates are rapidly cleaved by the enzyme 2'-phosphodiesterase (cf. the reference above mentioned to Baglioni C.).
Both endoribonuclease and 2'-phosphodiesterase are present in about the same amount in untreated cells as in cells treated with interferon.
When the cell is treated with interferon, the concentration of 2'-5' oligonucleotide polymerase which recognizes endoribonuclease and which interacts with viral replicative structures, increases.
When interferon is removed from the culture medium, the 2'-5' oligonucleotide polymerase activity declines and the cell loses its antiviral state.
The synthesis of proteins induced by interferon is transitory and therefore cells kept in tissue culture do not maintain enhanced levels of these proteins.
Researches have been undertaken to find synthetic analogs of 2'-5' oligoadenylates with increased activity compared to the activity of 2'-5' oligoadenylates induced in cells treated with interferon (Baglioni C. et al., 1981, Analogs of (2'-5')oligo(A). Endonuclease activation and inhibition of protein synthesis in intact cells, The Journal of Biological Chemistry, vol. 256, no. 7, p. 3 253-3 257).
It is to be pointed out that all the analogs which have been synthesized resort to modifications of the riboadenosine unit, for most of them, or to the use of arabinoadenosine.
The results obtained so far, with respect to enzymatic stability, for analogs of 2'-5' adenylates, constituted by chains containing several riboadenosines or of arabinoadenosines have allowed to define some of the structural requirements for endonuclease activation and inhibition of protein synthesis.
The conclusion which has been drawn so far, on the basis of the studies carried out on analogs of 2'-5' adenylates containing riboadenosine units is a mere hypothesis according to which some analogs of 2'-5' adenylates, in the riboadenosine series, could be responsible for some of the same effects (with respect to inhibition of protein synthesis) as the ones induced by interferon.
Applicants have now found new oligonucleotides having a structure different from that of the natural 2'-5' oligoadenylates and its known analogs having an interferon like activity, an increased duration of biological activity, a resistance to degradation by 2'-phosphodiesterase and a higher degree of protection.
It is thus an object of the invention to provide new oligonucleotides which can be recognized by the endoribonuclease, i.e. which can build up with endoribonuclease, an active complex.
It is another object of the invention to provide new oligonucleotides which are more resistant to degradation by 2'-phosphodiesterase.
It is also an object of the invention to provide new oligonucleotides which have an activity like interferon with increased duration of the biological activity.